If there was any evidence to prove that art is becoming a commodity, and even more so a consumer product, the excellent exhibition running at Tate Liverpool makes the issue crystal clear. 'Shopping: A Century of Art and Consumer Culture' runs through 23 March. This exhibition offers also a serious message; that actual shopping stores and malls can be established in certain harmony within our museums and galleries. That raises the difficult judgement of what authenticity or perfectibility constitutes, and how it affects the consumer. Could the Emin bed be marketed as a 'multiple', and can one commodify dirt and trash? This was the issue brilliantly addressed earlier by Tracey Emin: that decay, decomposition, and 'dropped' personalia are protected from sanitisation, rather than to be destroyed by this process. But the process of commodifying after the sell-by date is proving well nigh impossible to apply. Here, such works as Mike Bidlo's simulacrum of Warhol's famous Brillo Boxes, or the candescent shop windows of Christo, today reveal a soft core nostalgia. Archival photographs from 1920s' Germany remind us of the shop managers own pride in artful display, where banal objects such as saucepans can, displayed en masse, become supreme manifestations of object art: Saatchi, please note the stimulus potential of the site near Tate Modern.